Aluminum plating



March 22, 1960 E. R. BREINING ETAL 2,929,739

ALUMINUM PLATING Filed Nov. 7, 1958 14770, IVEXS ALUMINUM PLATING ElmerRobert Breining, Dayton, Wilbur M. Boiton, Piqua, and Fritz O.Deutscher, Dayton, Ohio, assignors, I by mesne assignments, to UnionCarbide Corporation, New York, N .Y., a corporation of New YorkApplication November 7, 1958, Serial No. 772,517

Claims. (Cl. 117-107) This invention relates to the deposition ofaluminum from volatilizable, heat decomposable aluminum bearingcompounds.

It has previously been suggested to utilize aluminum compounds in thegaseous state to procure deposits of aluminum metal and coatings ofaluminum. Ditficulties encountered have included the necessity for usingrelatively high temperatures to efiect the decomposition of the aluminumcompound; purity of deposit and thickness of deposit have also beenlimited and much effort has been expended to overcome these drawbacks.

. It has now been found that a reactive additive olefinic gas may beintroduced into the plating operation with the aluminum containingcompound to provide for decomposition of the compound at lowertemperatures and to materially improve film continuity in the case ofaluminum coatings on articles of steel, copper and the like.

In a specific application isobutylene is provided as a reactive gas withaluminum tri-iso'outyl as the plating gas. The function of theisobutylene is to react with hydrides of aluminum which tend to formwhen aluminum tri-isobutyl breaks down. The hydrides, which form eitherduring the plating process itself or in storage of the aluminumtri-isobutyl include aluminum hydride, aluminum di-isobutyl hydride, andaluminum monobutyl .hydride. The reaction of the isobutylene with thesehydrides tends to reproduce the tri-isobutyl in accordance with thefollowing exemplary reaction:

.showed a refinement in the grain size of the aluminum deposit. This isbelieved to be due to the microscopic dissolution of the aluminumsurface according to the equation previously cited.

Other aluminum containing compounds useful in conjunction with areactive additive olefiuic gas are: alumi- .num tri-isopropyl, aluminumtri-isoamyl, aluminum triisohexyl, and mixed aluminum alkyls such asdiethyl .;isopropyl aluminum, propyl di-isobutyl aluminum, ethyl propylisobutyl aluminum.

In general the object on which thealumlnum is to be r deposited in thepractice of the invention need not be heated above 700 F. in order toattain adequate deposition of aluminum; preferably the object is atabout 500 F. This is in contrast to processes wherein the olefin is notemployed and temperatures well above 700 F. and frequently above 1000 F.are required to secure adequate plating rates.

The invention will be more fully understood by reference to thefollowing detailed description and accompanying drawing wherein:

Figure 1 is a schematic view illustrating an apparatus arrangementuseful in the practice of the invention; and

Figure 2 is across section of a tube metallized in accordance with theinvention.

In the practice of the invention the substrate to be plated is suitablyde-oxidized, cleaned and preferably degreased prior to commencing anoperation; also, as noted hereinafter, the apparatus itself is evacuatedby purging with an inert gas.

Referring to the drawing the numeral 1 designates a conduit having avalve 2 and through which the metallizing gas is fed to the vaporizer 3.In the present instance the metallizing gas is commercial aluminumtriisobutyl and contains approximately 10 percent of aluminumtri-isobutyl hydride as used.

The vaporizer 3 is heated by means of an electrical coil 4 at atemperature of approximately 475 F. This metallizing gas enters thevaporizer in liquid form through a depending conduit 5. Simultaneouslyargon gas is introduced through conduit 6 having a valve 7 and isdirected toward the vaporizer 3. As the argon passes toward thevaporizer it mixes with isobutylene gas passing through the conduit 8having valve 9. The argon utilized is substantially oxygen free, testingless than 0.0005 percent oxygen by volume.

Within the vaporizer the argon and isobutylene mix with the aluminumtri-isobutyl which vaporizes and passes out through orifice 10. Aluminumtri-isobutyl hydride is a liquid and that portion of the liquid whichdoes not react with the isobutylene remains in the bottom of thevaporizer as indicated at 11. The isobutylene, however, serves to reactwith the tri-isobutyl hydride to produce tri-isobutyl, as already noted.The argon with the aluminum tri-isobutyl passes outwardly through theorifice 10 towards the article to be plated, designated at 12.

As shown in Figure 1 this article is a tube of copper which is sealed atone end to a conduit 13 having a valve 14. At its other extremity thetube 12 is sealed to an exhaust conduit 15 having a valve 16.Thealuminum tri-isobutyl flows through open valve 14 to the copper tube,which is itself maintained at a temperature of about 525 F. by anysuitable heating means such as resistance heater 17. The aluminumtri-isobutyl decom poses, depositing aluminum on the interior. of thecopper tube as indicated at 18. Normally a thickness of 1% mil isreadily achieved over the interior of the copper tube (0 I.D.) within 3hours.

The gas flow rates at F. and atmospheric pressure to achieve thisdeposition are about:

this isobutyl aluminum flow is equivalent to about cc. per minute of theliquid tri-isobutyl. Suitably the carrier gas (argon) and theisobutylene are heated prior to their introduction to the system to atemperature of 200-220 vF.

Gases of decomposition pass outwardly through valve 16 of the conduit 15together with undecomposed aluminum tri-isobutyl.

For purposes of complete operation a by-pass conduit 9 provided withvalve 2%) is located in the conduit 14. For thepurposes of initialpurging the apparatus of air and moisture, prior to metallizing, anintermediate conduit 21, provided with a valve 22, is located in theconduit 14. Thus to purge the apparatus, through the vaporizer, it ismerely necessary to close valve 14 and to open valves 22 and 7, and topass a gas such as argon through the equipment. When the vaporizer andthe lines leading thereto are sufi'iciently clear, valves 14 and 16 maybe opened, with valves 29 and 22 closed, to completely purge theapparatus by permitting argon flow through valve 14, the coppersubstrate 12 and valve 16also.

Suitably the operation of metallizing is effected at atmosphericpressure, although pressures as low as mm. of mercury may be employed.As may be noted from Figure 2 the aluminum coating on the interior ofthe tube 12 is substantially uniform.

Other gases may be used as the carrier in the gas plating process, forexample, nitrogen and helium.

By way of further example propylene may be substituted for theisobutylcne and nitrogen for the argon under the same conditions as setforth hereinbefore. The nitrogen employed has less than 0.0005 percentoxygen by volume.

While liquids such as cyclopentadiene have characteristics renderingthem useful as substitutes for isobutylene and propylene, they are lessconvenient to handle, requiring vaporization for admixing with thedecomposable aluminum compound in the vaporizer.

It will be understood that this invention is susceptible to modificationin order to adapt it to difierent usages and conditions and accordingly,it is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claims.

What is claimed is:

1. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable aluminum alkyl compound; theimprovement which comprises: intermixing in the gaseous state a heatdecomposable aluminum containing compound which tends to form hydridesof aluminum and an unsaturated compound capable of reacting with suchhydrides to form the heat decomposable aluminum compound.

2. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable aluminum alltyl compound; theimprovement which comprises: intermixing in the gaseous state a heatdecomposable aluminum alkyl with an olefin.

3. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable aluminum allzyl compound; theimprovement which comprises: intermixing in the gaseous state a heatdecomposable aluminum alkyl and an alpha olefin.

4. In an aluminum deposition process, wherein a substrate, is heated inthe presence of a heat decomposable aluminum alkyl compound; theimprovement which comprises: the step of intermixing in the gaseousstate a heat decomposable aluminum alkyl and isobutylene.

5. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable alumnium alkyl compound; theimprovement which comprises: the step of intermixing in the gaseousstate a heat decomposable aluminum alkyl and propylene.

6. In an aluminum deposition process, wherein a sub.- strate is heatedin the presence of a heat decomposable aluminum alkyl compound; theimprovement which comprises: the step of intermixing in the gaseousstate a heat decomposable aluminum alkyl and ethylene.

7. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable aluminum alkyl compound; theimprovement which comprises: the step of intermixing in the gaseousstate a heat decomposable aluminum alkyl and 3 methyl-butene-l.

8. In an aluminum deposition process, wherein a substrate is heated inthe presence of a heat decomposable aluminum alkyl compound; theimprovement which comprises: the step of intermixing in the gaseousstate a heat decomposable aluminum alkyl and cyclopentadiene.

9. A process for the deposition of aluminum which comprises the steps ofheating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature sufficient to decompose a gaseousaluminum alkyl, contacting the heated object with a gas flow containinga heat decomposable aluminum alkyl and a gaseous olefin capable ofreacting with such alkyl to form a heat decomposable compound to therebyoccasion deposition of the aluminum on the heated object, continuing thegas flow to the heated object to build up a continuous film of aluminumon the object, and thereafter removing the object from the gas flow.

10. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature sufiicient to decompose a gaseousaluminum alkyl, contacting the heated object with a gas flow containinga heat decomposable aluminum alkyl and isobutylene with a carrier gas tooccasion deposition of the aluminum on the heated object, continuing thegas fiow to the heated object to build up a'continuous film of aluminumon the object, and thereafter removing the object from the gas flow.

11. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature sufiicient to decompose a gaseousaluminum alkyl, contacting the heated object with a gas flow containinga heat decomposable aluminum alkyl and propylene with a carrier gas tooccasion deposition of the aluminum on the heated object, continuing thegas flow to the heated object to build up a continuous film of aluminumon the object, and thereafter removing the object from the gas flow.

12. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature sufficient to decompose a gaseousaluminum alkyl, contacting the heated object with a gas flow containinga heat decomposable aluminum alkyl and isobutylene with argon tooccasion deposition of the aluminum on the heated obiect, continuing thegas flow to the heated object to build up a continuous film of aluminumon the object, and thereafter removing the object from the gas flow.

13. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature sufficient to decompose a gaseousaluminum alkyl, contacting the heated object with a gas flow containinga heat decomposable aluminum alkyl and propylene with nitrogen tooccasion deposition of the aluminum on the heated object, continuing thegas flow to the heated object to build up a continuous film of aluminumon the object, and thereafter removing the object from the gas flow.

14. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature of between about 500 F. to about700' R, contacting the heated object with a gas flow containing a heatdecomposable aluminum alkyl and a gaseous olefin capable of reactingwith such alkyl to form a heat decomposable compound to thereby occasiondeposition of the aluminum on the heated object, continuing the-gas flowto the heated object to build up a continuous film of aluminum on theobject, and thereafter removing the object from the gas flow.

15. A process for the deposition of aluminum which comprises the stepsof heating an object on which the aluminum is to be deposited in anevacuated atmosphere to a temperature of about 525 F., contacting theheated object with a gas flow containing a heat decomposable aluminumalkyl and a gaseous olefin capable of reacting with such alkyl to form aheat decomposable compound 6 to thereby occasion deposition of thealuminum on the heated object, continuing the gas flow to the heatedobject to build up a continuous film of aluminum on the object, andthereafter removing the object from the gas References Cited in the fileof this patent UNITED STATES PATENTS Davis et al Nov. 25, 1952 2,847,320Bufiofi Aug. 12, 1958

1. AN ALUMINUM DESPOSITION PROCES, WHEREIN A SUBSTRATE IS HEATED IN THEPRESENCE OF A HEAT DECOMPOSABLE ALUMINUM ALKYL COMPOUND, THE IMPROVEMENTWHICH COMPRISES: INTERMIXING IN THE GASEOUS STATE A HEAT DECOMPOSABLEALUMINUM CONTAINING COMPOUND WHICH TENDS TO FORM HYDRIDES OF ALUMINUMAND AN UNSATURATED COMPOUND